1. Field of the Invention
The present invention relates to a surface discharge type plasma display panel (PDP) in which main electrodes making a pair extend in parallel as row electrodes defining rows of a screen.
It is said that a ratio of a main electrode area and a cell area (an area ratio) is better to be smaller for improving a light emission efficiency (1m/W) that is a light emission quantity (luminous flux) per a unit power consumption in a plasma display panel. In xe2x80x9cThe latest in Technology of Plasma Display,xe2x80x9d (Mikoshiba, ED Research Co.) the following equation is disclosed.
light emission efficiency=1/(1+cxc3x97discharge current density),
where c is a constant.
Two of the reasons the light emission efficiency is improved are as follows. First, non-effective power consumed for charging a capacitance between the electrodes is reduced. Secondly, the discharge current decreases along with the decrease of the area ratio, and self-absorption of a vacuum ultraviolet light by discharge gas decreases so that excitation efficiency is enhanced.
However, if the width of the main electrode is reduced for decreasing the area ratio, the gap length of the surface discharge is increased. In this case, although the capacitance between the electrodes decreases, a discharge starting voltage increases and a voltage margin of driving decreases.
The increase of the cell number for a wide screen and a high definition causes an increase of power consumption. The reduction of the power consumption is important from a viewpoint of reducing generation of heat. It is required to satisfy both securing an operation margin for a stable display and improving the light emission efficiency.
2. Description of the Prior Art
FIG. 13 is a plan view showing the conventional electrode structure. FIG. 14 is a perspective view showing an inner structure of the conventional plasma display panel.
The illustrated plasma display panel 9 has a structure disclosed in Japanese unexamined patent publication No. 9-50768. Main electrodes Xq, Yq, a dielectric layer 17 and a protection film 18 are provided on the front side glass substrate 11. On the backside glass substrate 21, there are provided address electrodes A as row electrodes, an insulator layer 24, partitions 29 for defining a discharge space 30, and fluorescent layers 28R, 28G and 28B for color display. Each of the main electrodes Xq, Yq includes a transparent conductive film 41q and a metal film 42q. The main electrodes Xq, Yq are arranged alternately at a constant space (a surface discharge gap) in the column direction. The gap direction of the surface discharge gap, i.e., the direction in which the main electrodes Xq, Yq face each other is the column direction. The discharge space 30 is filled with a two-component gas such as neon and xenon.
In the plasma display panel 9, the partition 29 that divides the discharge space 30 in each column has a ribbon shape meandering regularly in a plan view. As shown in FIG. 14, each partition 29 is meandering at a constant pitch and width in a plan view, and is arranged so that the distance between the neighboring partitions 29 becomes smaller than a constant value periodically along the column direction. The constant value is a distance that can suppress the discharge and is determined by the discharge condition such as a gas pressure. Since the partitions 29 are disposed separately, the space (a column space) 31 between the neighboring partitions is continuous over the all rows of the screen. Thus, easiness of the drive in each column by priming, uniformity of the printing state of the fluorescent layer and easiness of the exhausting process in manufacturing can be realized. In the plasma display panel 9, a red fluorescent layer 28R, a green fluorescent layer 28G and a blue fluorescent layer 28B are arranged in this order for each column. The light emission color of each row in a column is the same.
A portion (a narrowing portion) 31B of the column space 31 in which the width in the row direction is small cannot generate the surface discharge easily, so a portion (enlarging portion) 31A having a wide width substantially contributes the light emission. Therefore, a cell that is a display element is disposed at every two columns in each row. Noting the neighboring two rows, the column in which a cell is disposed changes alternately one by one column. Namely, cells are arranged in a staggered pattern both in the row direction and the column direction. In the plasma display panel 9, the neighboring three cells of red, green and blue colors constitute a pixel. The arrangement format of the color display by the three colors is a triangle (delta) format. The triangle arrangement has an advantage for high definition compared with an inline arrangement since the width of the cell is larger than one third of the pixel pitch in the row direction. In addition, it can perform a high intensity display since a ratio of non-emission area of the screen is small.
In the conventional structure, the shape of the main electrodes Xq, Yq in a plan view is like linear ribbon having a constant width over the full length of the screen, and the main electrodes Xq, Yq are close to each other in the narrowing portion 31B as well as the enlarging portion 31A of the column space 31. Therefore, an error discharge can be generated in the narrowing portion 31B. If attempting to prevent the error discharge completely by setting the drive voltage, the operation margin will become small. It is also a problem that a waste of power consumption for charging a capacitance between the electrodes is large.
The object of the present invention is to prevent the interference of discharge between the rows securely without decreasing the operation margin. Another object of the present invention is to reduce a capacitance between electrodes. Still another object of the present invention is to reduce a discharge current so as to improve a light emission efficiency.
In the present invention, the shape of the main is selected so that an electrode area ratio at a narrowing portion in a column space is smaller than an electrode area ratio at an enlarging portion, and the maximum value of the electrode gap between rows at the narrowing portion is larger than the minimum value of the electrode gap at the enlarging portion (i.e., surface discharge gap length). If the electrode area ratio at the narrowing portion is small, the diffusion of the discharge along the electrode is suppressed so that the interference of the discharge in the column direction is prevented. It is the best that the main electrode is provided so that the electrode area ratio becomes zero, i.e., so as to avoid the narrowing portion. In addition, by enlarging the electrode gap between rows at the narrowing portion for a part or the entire of the opposing area of the electrodes, a capacitance between the electrodes is reduced. Thus, a waste of power consumption is reduced so that the light emission efficiency is improved.
In the present invention, the main electrode is formed in the shape having a belt-like portion extending in the row direction and a half circle portion protruding toward the enlarging portion of each column. The half circle portion opposes the other half circle portion of the neighboring main electrode so as to form a surface discharge gap, The electrode area in the cell decreases by the extent of the gap between the half circle portion and the belt-like portion. As a result, the discharge current decreases so that light emission efficiency is improved. It is not necessary to increase the surface discharge gap length for decreasing the electrode area. Namely, a predetermined operation margin can be secured. By increasing the number of lighting times per a period, the drop of the intensity due to the decrease of the discharge current can be compensated. It is preferable for the intensity to form the half circle portion with a transparent conductive film such as ITO or Nesa when arranging the main electrode at the front side of the discharge space. If the main electrode is arranged at the rear side of the discharge space, consideration for light shield by the electrode is not necessary, so the belt-like portion and the half circle portion can be formed with a metal film. In this case too, the belt-like portion reduces the line resistance of the electrode. When omitting the belt-like portion, the electrode shape becomes a meandering belt-like and the entire length becomes larger than the screen, so the voltage drop becomes outstanding.
According to a first aspect of the present invention, a plasma display panel includes a plurality of partitions being apart from each other and defining a discharge space of each column in a screen, and a column space defined by the partitions. The column space is narrowed periodically along the column direction. A surface discharge gap is formed at each enlarging portion of the column space. A pair of main electrodes for surface discharge is provided, and each of the main electrodes includes a belt-like bus portion extending in the row direction of the screen and plural gap forming portions protruding from the bus portion in the column direction at each intersection with the partition.
According to a second aspect of the present invention, the arrangement distance of the plural gap forming portions in the row direction is substantially equal to the partition distance of the narrowing portion of the column space or is larger than the same.
According to a third aspect of the present invention, the bus portion is made of a metal film, and each of the plural gap forming portions is made of a transparent conductive film that is patterned so as to protrude from the bus portion to both sides in the column direction.
According to a fourth aspect of the present invention, each of the main electrodes that make an electrode pair for surface discharge includes a belt-like bus portion extending in the row direction of the screen and plural gap forming portions protruding from the bus portion toward the enlarging portion in the column direction in each column space.
According to a fifth aspect of the present invention, the arrangement distance of the plural gap forming portions in the row direction is substantially equal to the partition distance of the narrowing portion of the column space or is larger than the same.
According to a sixth aspect of the present invention, the bus portion is made of a metal film, and each of the plural gap forming portions is made of a transparent conductive film that is patterned in the belt-like shape extending in the row direction while meandering in the column direction.
According to a seventh aspect of the present invention, each of the plural gap forming portions includes a first linear pattern extending in the row direction at a distance from the bus portion and two second linear patterns that connect each end of the first linear pattern to the bus portion.
According to an eighth aspect of the present invention, both ends of the first linear pattern protrude from the second linear pattern connecting the first linear pattern in the row direction.
According to a ninth aspect of the present invention, each of the plural gap forming portions is patterned in such a shape that opposing sides of the plural gap forming portions and the other main electrode forming the surface discharge gap together are not parallel to each other.
According to a tenth aspect of the present invention, each of the plural gap forming portions has an arc shape whose ends are connected to the bus portion.
According to an eleventh aspect of the present invention, a plasma display panel includes a plurality of partitions being apart from each other and defining a discharge space of each column in a screen and a column space defined by the partitions. The column space is narrowed periodically along the column direction and a surface discharge gap is formed at each enlarging portion of the column space. A pair of main electrodes for surface discharge is arranged at the front side of the discharge space. Each of the main electrodes includes a belt-like bus portion extending in the row direction while meandering in the column direction along the partition in a plan view, and plural gap forming portions protrudes from the bus portion toward the enlarging portion in the column direction in each column space. The bus portion is made of a metal film. Each of the plural gap forming portions has a belt-like shape connected to the bus portion only at both ends, and being made of a transparent conductive film extending in the row direction while meandering in the column direction.
According to a twelfth aspect of the present invention, each of the main electrodes includes a belt-like bus portion extending in the row direction while meandering in the column direction along the partition in a plan view and plural linear belt-like gap forming portions protruding in the row direction at each enlarging portion of the column space. Each of the main electrodes is patterned in the shape having a gap between each of the plural gap forming portions and the bus portion. The bus portion is made of a metal film. The plural gap forming portions are made of a transparent conductive film.
According to a thirteenth aspect of the present invention, each of the plural main electrodes is made of the metal film and at least two linear belt-like transparent conductive films extending in the row direction over the full length of the screen while being at a distance from each other.
According to a fourteenth aspect of the present invention, the transparent conductive film is patterned in the shape having a connection pattern for connecting the center of each gap forming portion in the row direction to the bus portion.